This invention relates to the field of rotary bearings and more specifically to the field of rotary liquid bearings for bioprocessing equipment.
Radial bearings and axial thrust bearings are known. Radial bearings allow one member to rotate with respect to another member. Axial thrust bearings allow a member to rotate and, in addition, provide an axial force (thrust), perpendicular to the direction of rotation.
Rotating biological equipment is known, and bearings are used in such equipment. See, for example, U.S. Pat. Nos. 3,647,632 (bearing 22), 4,302,330 (bearing 60), and 4,675,106 (bearing pins 29 and 42); European Published Application 0 112 152 (bearing 78 with tapered surface 79 in FIGS. 1 and 2 and bearing 104 in FIGS. 7 and 8); PCT Published Applications WO 86/01426 (bearing 44), WO 85/04112 (bearings 102 and 103), WO 86/06293 (pivot pins 29 and 42, and bearing surfaces 30, 45, and 46), WO 88/01194 (pivot pins 20 and 22 and pivot bearing 150), and WO 85/02783 (e.g., bearings 152a and b in FIG. 14); Sherwood, "Desalination by Reverse Osmosis," I&EC Fundamentals, Volume 6, pages 2-12 (1967); Sulzer Biotechnics, "Dynamic Pressure Filtration," two-page brochure (1985); Thayer, "Spin Filter Device For Suspension Cultures," chapter 12 in Kruse (editor), Tissue Culture Methods And Applications, pages 345-351 (1973); Himmelfarb, "Spin Filter Culture: The Propagation of Mammalian Cells in Suspension," Science, pages 555-557 (May 1969); and Tobler, "Dynamic Filtration--The Engineering Concept of the Escher Wyss Pressure Filter," Filtration & Separation, Volume 16, pages 630-632 (November/December 1979). Afeyan, "Continuous Adsorptive Extraction Of Proteins," Bioprocess Engineering Colloquium, Winter Annual Meeting of ASME, pages 101-104 (December 13-18, 1987) discuss rotary devices, including those of Membrex, the assignee of this application.
There are different bearing configurations. For example, the end of a rotating shaft may ride and rotate within a concavity in a stationary member. If the corresponding adjacent surfaces of the shaft and stationary member do not produce too much frictional heat because they are smooth and lubricious enough and/or the speed of rotation is slow enough, the surfaces may not bind. A lubricating fluid may be used between the surfaces. Mechanical bearings, such as ball bearings, are sometimes used. Such bearings also perform a centering function, that is, they laterally center the moving member during rotation so that its axis of rotation remains substantially coincident with the longitudinal axis of the housing or framework in which it was designed to rotate.
Liquid bearings, in which the corresponding adjacent rotating and stationary surfaces of the device are separated sufficiently by a liquid film, are also known. In such bearings, there is essentially only "liquid friction" and not "dry friction" or "semi-dry friction." Liquid bearings that center the rotating member are known but apparently have not been used in rotating equipment processing biological fluids. (See Fuller, Theory and Practice of Lubrication for Engineers, page 192 et seq., particularly FIG. 124 (John Wiley & Sons, Inc. 1956), which book is hereby incorporated in its entirety.) That may be because of concerns about contaminating the biological substances with a bearing fluid.
In FIGS. 1 and 2 of EPO 0 112 152, shoulder 80 of rotating filter 14 is urged downward against tapered surface 79 of bearing 78. That keeps filter 14 centered and creates a fluid-tight seal between the filtrate (plasma) in passageway 58 and remaining unfiltered blood (retentate) in concavity 84. In FIGS. 7 and 8, end bearing 104 projects up into manifold 94 and O-ring 102 provides the required fluid-tight seal and keeps rotating filter 14 centered.
In FIG. 1 of U.S. Pat. No. 3,647,632 lower shaft 21 rides on foot bearing 22. In PCT published application WO 85/02783 the rotating filters are mounted for rotation as by bearings 152 in FIG. 14. Those bearings also keep the filter centered. In FIGS. 17 and 18 of the same application, the bottom bearings comprise extensions of the bottoms of the rotating filters, which extensions ride within mating concavities in the bottom housing members 168.
However, in none of these devices is a liquid bearing used to keep the rotating member laterally centered. In none of these devices is a liquid bearing used to keep a rotating member laterally centered where the rotating member is free to become off-center during rotation. In none of these devices is a liquid bearing used to keep the free end of a rotating member laterally centered and also provide axial thrust during rotation. In none of these devices is a liquid bearing used as the only way to substantially reduce the shear forces on biological substances in fluids as they contact or otherwise pass through a bearing.